Sensory inputs to the olfactory system are initially processed by neural circuits in olfactory bulb (OB) glomeruli. This circuitry is targeted by centrifugal inputs from neuromodulatory centers. OB output via mitral/tufted (MT) cells shows remarkable modulation of sensory responses in the awake animal. Knowing how these earliest stages of odor information processing are modulated is critical to fully understanding olfactory system function. This project will investigate - for the first time - how acetylcholine (ACh) and serotonin (5HT) modulate sensory processing in glomerular circuits. The research builds on recent advances in our understanding of these circuits and their importance in shaping OB output. The project will integrate information from OB slices and anesthetized and awake head-fixed mice. This multidimensional approach aims to link the modulation of glomerular circuits to the activation of specific neuromodulatory systems - cholinergic inputs from the diagonal band and serotonergic inputs from the raphe nuclei. Our working hypothesis is that ACh and 5HT differentially modulate glomerular processing to shape both pre- and postsynaptic inhibition as well as MT cell excitability. We further hypothesize that ACh modulation reduces the impact of sensory input while at the same time increasing the excitability of MT cells. This could limit odor detection but increase discrimination ability. The proposed research is a highly integrated effort from two established investigators to understand the modulation of early olfactory processing at levels ranging from cells and circuits to single neurons in anesthetized and unanesthetized animals.